A classic experiment to demonstrate the curvature of a body of water is to place markers (like flags) a fixed distance above the water in a straight line, and then view them along that line in a telescope. If the water surface is flat then the markers will appear also in a straight line. If the surface of the water is curved (as it is here on Earth) then the markers in the middle will appear higher than the markers at the ends. Here's a highly exaggerated diagram of the effect by Alfred Russel Wallace in 1870:

This is a difficult experiment to do as you need a few miles for the curvature to be apparent. You also need the markers to be quite high above the surface of the water, as temperature differences between the water and the air tend to create significant refraction effects close to the water.

However Youtuber Soundly has found a spot where there's a very long line of markers permanently fixed at constant heights above the water line, clearly demonstrating the curve. It's a line of power transmission towers at Lake Pontchartrain, near New Orleans, Louisiana.

The line of power lines is straight, and they are all the same size, and the same height above the water. They are also very tall, and form a straight line nearly 16 miles long. Far better than any experiment one could set up on a canal or a lake. You just need to get into a position where you can see along the line of towers, and then use a powerful zoom lense to look along the line to make any curve apparent

One objection you might make is that the towers could be curving to the right. However the same curve is apparent from both sides, so it can only be curving over the horizon.

Case closed? You would think so. But some raised the possibility that the images are faked - they are taken from a freeway, so require a little effort to duplicate. Soundly then went to incredible lengths to demonstrate they are not fake. Ultimately he did a live stream of himself taking the video, then driving to a cafe where he uploaded it to Youtube.
Here's the live stream:

People have asked why the curve is so apparent in one direction, but not in the other. The answer is compressed perspective. Here's a physical example:

That's my car, the roof of which is slightly curved both front to back and left to right. I've put some equal sized chess pawns on it in two straight lines. If we step back a bit and zoom in we get:
Notice a very distinct curve from the white pieces, but the "horizon" seems to barely curve at all.

Similarly in the front-back direction, where there's an even greater curve:
If the pieces were actually level, placed on a similar length line:
Then straight lines would remain straight, and it would look like this, even with extreme perspective compression.

Another physical example of compressed perspective that many people will be familiar with is looking along a pool cue to see if it is straight.

Pool cues are manufactured straight (in theory), but over time they sometimes develop slight bends - especially those that are subject to years of use, like in pubs and bars. This can occur for a few reasons, but is often just warping of the wood in cheap cues. So people often look along the cue, utilizing perspective compression to check.

And if we look straight along it from above then it still looks straight - just like the towers on Pontchartrain are in a straight line.

But looking from the side, we can see there's actually a curve

This is a physical downward curve in the cue. The tip of the cue is wedged under the block, and there's a small support about a foot from the tip. The weight of the handle end of the cue is making it bend downward. It's not a lot though (like the very slight curve of the earth) so you can only see it from this perspective.

This effect is magnified if we move the camera back a long way and then zoom in at a shallow angle. This is important, as it posible to get similar looking shots of things like pylons with very different zoom settings (technically it's the distance to the camera that create the effect, but you need to zoom in to see it). At lower zoom the curve is concentrated more in the distance, and so is harder to see. At higher zooms the curve is much more evenly spread over the whole image.
And again we see the same "up and over" curve from both sides.

Yet viewed along its length from that distance, the cue appears straight.

This proves, like with the Pontchartrain towers, the only curve is vertical.

The spot from which these photos was taken is on Interstate 10, and is not really a safe (or even legal) place to stop. I'd recommend photos or video be taken by a passenger while the driver concentrates on driving.

Hi mick,
first time poster here, im on the search for evidence of the globe vs the flat earth. ive mostly found nothing to support a flat earth and always keen to see the globe evidence. This post was great until the pool cue bit. Thats what im posting about before posting it on. are the pics yours? is the cue curved? can you show a pic of it curving the other way? and then zoom in? just to show that its definately not the camera causing the curve in the cue? much appreciated for any reply,
Carl.

Hi mick,
first time poster here, im on the search for evidence of the globe vs the flat earth. ive mostly found nothing to support a flat earth and always keen to see the globe evidence. This post was great until the pool cue bit. Thats what im posting about before posting it on. are the pics yours? is the cue curved? can you show a pic of it curving the other way? and then zoom in? just to show that its definately not the camera causing the curve in the cue? much appreciated for any reply,
Carl.

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This is a physical downward curve in the cue. The tip of the cue is wedged under the block, and there's a small support about a foot from the tip. The weight of the handle end of the cue is making it bend downward. It's not a lot though (like the very slight curve of the earth) so you can only see it from this perspective.

The pics are mine (it's an old junk cue I had in the garage, you can get them at a thrift store for $1). I'm not sure what you mean by "curving the other way" - sideways?

Try this experiment: Pick up an envelope, notice the edge is straight. Then hold it up to your eye and look along the length of the edge of the envelope, and you will notice it is not.

Compressing the perspective does not create a curve - it just magnifies an existing curve.

i see what your saying i was hoping the cue could be rotated 180 degrees and be pointing up. i can see now by the way you created the curve this is not possible. im trying to preempt the nay sayers. thanks for your quick reply guys.
Carl.
p.s. maybe you could do the same pictures with a straight metal bar and a slightly curved one to show the camera dose not create the curve?

With the horizon at an angle, the camera at a greater distance from the base of the line, and the atmospheric distortion, it is harder to see the curve, but if you take a straight edge (I used a handy envelope from my junk mail) and try lining up the very bottom of the leftmost pylon with the far right pylons when the picture is zoomed in, you'll find that it's impossible to do it without having a little bit of lake showing under the middle pylons.

Of course, now I'm curious about whether tilting the camera or moving it away from the line would diminish the curvature effect for the chess pieces demonstration too...

Oh yes, this thread should be a definitive goto page for curvature proof. I have been following the frantic scramble of flat-earthers attempting to discredit Soundly's numerous photo/video proofs of the towers. But his YT channel is scattered to go thru, and not all his videos are clear examples, so I am glad you put this thread up. The transmission line images are the best disproof of flat earth. Debunkers do not always realize [that] it is best to use examples like this that are very simple and visual, with no math or graphics or reference to "authority." Soundly said he will take more clear photos in fall when there is less haze.

With the horizon at an angle, the camera at a greater distance from the base of the line, and the atmospheric distortion, it is harder to see the curve, but if you take a straight edge (I used a handy envelope from my junk mail) and try lining up the very bottom of the leftmost pylon with the far right pylons when the picture is zoomed in, you'll find that it's impossible to do it without having a little bit of lake showing under the middle pylons.

Of course, now I'm curious about whether tilting the camera or moving it away from the line would diminish the curvature effect for the chess pieces demonstration too...

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On reflection, I think that a part of the not-much-curve problem in this one example is due to near-horizon refraction actually raising the far towers (and the far shore) up.

The resolution to such problems is to take photos in lots of different atmospheric conditions, as Soundly already has done.

The Earth's circumference is roughly 25,000 miles. Standing at sea level, a 6ft tall person would see only 3 miles to the horizon. The tops of many ships would still be visible, but any boat beyond the horizon would not have a visible waterline.
The Lake Pontchartrain Causeway has a 15 foot clearance. Adding the height of an average person's standing eye level will give a view of 5.6 miles to horizon. Again, the tops of buildings & trees may be seen many miles away, but not the shoreline beyond 5.6 miles.
In order to see one shoreline to another across Lake Pontchartrain, looking down the 24 mile causeway, you'd need to be looking from 365 feet, equivalent to standing on the roof a 35 story building.
So yea, the power lines are built to the Earths curvature, so is the damned bridge you were driving on.
Even my 4 year old daughter realizes you can see further if you climb higher.
Why does this need to be explained? Why do people find this somehow fascinating? Why am I even replying to this?
You are ALL goofs.
(Oh, my calculations were assuming the Earth is a perfect sphere, which it's not, but the margin of error is inconsequential for such small measurements. The numbers are true.)

On reflection, I think that a part of the not-much-curve problem in this one example is due to near-horizon refraction actually raising the far towers (and the far shore) up.

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Ah, thanks, that answers my earlier question. I wasn't sure if atmospheric refraction only perceptibly "raises" objects at a sufficient distance (like celestial bodies), or whether it is already noticeable near the horizon itself.

EDIT: Actually, upon closer inspection of the picture in your OP, some refraction must be at play as well: Near the horizon, the curve appears to flatten, almost to the point of curling upwards (I've slightly exaggerated the effect):

Assuming (which I do) that the power line is level with Earth's surface and the actual downward curve is constant, refraction would seem to be the only conceivable explanation for this effect.

The line of power lines is straight, and they are all the same size, and the same height above the water. They are also very tall, and form a straight line nearly 16 miles long. Far better than any experiment one could set up on a canal or a lake. You just need to get into a position where you can see along the line of towers, and then use a powerful zoom lense to look along the line to make any curve apparent

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Just playing devil's advocate, is there any proof that the towers are all the same height? I could see people trying to claim that they get smaller along the line, creating the impression of a curve. Ideally it would be good to take photos from the other end of the line, too.

That end doesn't have any handy roads, but Google "Street View" does have pics from a boat there:

Just playing devli's advocate, is there any proof that the towers are all the same height?

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I was thinking that we could get someone out on a boat armed with a laser range finder/hypsometer (like this

Source: https://www.youtube.com/watch?v=SAUL76gEIUo
) to measure height of the next tower from a standardized position at the previous tower, but I suppose that given the number of towers you'd run into some degree of inconsistency due to the tides from the start of the run to the end. Maybe you could spot check it, maybe even skip some of the closer ones and focus on those closer to the horizon from the road?

Just playing devli's advocate, is there any proof that the towers are all the same height?

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I think your pic from the other end pretty much demonstrate that. But you can also look at the towers in GE images. They are taken from different angles, but you can still see the base and upper arm spans are the same between towers

The great thing about these observations is that the towers are not going anywhere. It's a shame the viewpoint is not more accessible, but the observations are still going to be repeated with increasing accuracy, and under even better weather conditions.

This thread is going somewhat viral on facebook. 17,000 shares and counting.

Update: 31,000 now! The push was getting shared by the Skeptics Guide to the Universe this morning. Hopefully this will direct the right people to Soundly's videos.

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52,000 Facebook shares now, and nearly 300,000 views of this thread. 30,000 views of the first Soundly video I linked to. Extrapolating from the 850 shares, 118K reached from my original FB post, that means it reached about 7 million people on Facebook. I think it's safe to say that pretty much everyone in the Flat Earth community (a tiny fraction of those 7 million) will have heard of Soundly's demonstration by now.

So there's going to be some blowback. Expect more "Soundly Debunked" videos. Again though the beauty of it is that the towers are fixed. Eventually they will have to stop saying "fake", and either admit that the lake is curved, or try to shoehorn yet another example into the "bendy light"/"perspective" catchcall.

I disagree here. When looking carefully by aligning the outer columns from both sides it seems to me that towers are curving slightly to the right (east side).

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I agree, there's a very slight curve to the right. However that does not change the fact that the downwards curve is visible (and seem more or less identical) from both sides. If the visible downward curve were the result of a purely horizontal curve, then from the other side it would be an upward curve.

Since the curve is pretty much the same from both sides, then that means it's largely the result of vertical curvature - i.e. over the horizon.

Consider this curved line of perfectly level identical chess pieces:

When it curves away from the camera, it looks like it's going up and over:
But from the other side it looks like it's going down and up.

I agree, there's a very slight curve to the right. However that does not change the fact that the downwards curve is visible (and seem more or less identical) from both sides. If the visible downward curve were the result of a purely horizontal curve, then from the other side it would be an upward curve.

Since the curve is pretty much the same from both sides, then that means it's largely the result of vertical curvature - i.e. over the horizon.

Consider this curved line of perfectly level identical chess pieces:

When it curves away from the camera, it looks like it's going up and over:
But from the other side it looks like it's going down and up.

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Yes, I agree somewhat with you. However, chess pieces can not simulate the distances nor visual effects we have in video, only proof of concept. The only way to be absolutely sure is to having the last tower in view perfectly visible.

But there is one more chance: Big tower in the distance.
If we could find somewhere how this distant tower looks like when in complete view we could scale & compare it and see how much of it is hidden by horizon making it fairly convincing proof of the true shape of planet Earth along with the power lines towers. Two evidences side by side on the same photo.

Yes, I agree somewhat with you. However, chess pieces can not simulate the distances nor visual effects we have in video, only proof of concept. The only way to be absolutely sure is to having the last tower in view perfectly visible.

But there is one more chance: Big tower in the distance.
If we could find somewhere how this distant tower looks like when in complete view we could scale & compare it and see how much of it is hidden by horizon making it fairly convincing proof of the true shape of planet Earth along with the power lines towers. Two evidences side by side on the same photo.

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The tall tower (GPS: 30°17'37.59"N, 90°18'38.64”W) is listed in FAA Obstacle data under the reference number ORS# 22-001038 which provides the height of the tower at 210ft (above ground level) and 211ft (above mean sea level).
from

The power lines are a dramatic example, but the view from the freeway is a bit dangerous, so here's a much safer location a few miles away, the Little Tensa Bayou under/between the Atchafalaya Basin Bridge